When sampling in a subsea production line where several phases (oil, water, and/or gas) are flowing and only a specific phase is wanted, the sampling process relies on an ability to separate the phases and keep the desired phase while rejecting the unwanted phases. The phase separation can be achieved in a separator or elsewhere. However, in some instances, the phase separation is very difficult to perform within a reasonable amount of time, particularly when the phases are mixed as an emulsion. In such cases, de-emulsifying additives can be added to the mixture to carry out the separation. The amount of de-emulsifier is typically relatively small, on the order of several ppm, and should be added continuously into the flow. The injection pressure is high, typically the well pressure. In subsea operations the pump is immersed in a deep-sea environment.